This invention relates to a sequence control circuit for automatically controlling the sequence of events in an industrial process or system.
The invention has particular application to the control of the charging of coke ovens with coal where the lid has to be raised before the oven is charged and then replaced as quickly as possible after the charge is made.
In our co-pending U.S. Pat. application Ser. No. 394,528 filed Sept. 5, 1975 now U.S. Pat. No. 3,966,060 we describe and claim a lifting apparatus for removing and replacing an object in a fixed location in which the lifting apparatus includes an arm carrying at one end engaging means for the object to be lifted, first rotating means for the arm, lifting and lowering means for the arm and second rotating means adapted to cause at least partial rotation of the engaging means.
APPARATUS IS THEREIN SPECIFICALLY EMBODIED IN AN ARM WHICH SWIVELS OVER A COKE OVEN, ENGAGES A LID OF THE OVEN, TWISTS IT, LIFTS IT AND SWINGS IT OUT OF THE WAY OF A CHARGING HOPPER WHICH FILLS IT AND THEN, AFTER FILLING, SWINGS THE LID BACK AND LOWERS IT IN POSITION BEFORE OSCILLATING IT TO SETTLE IT IN AND THEN FINALLY DISENGAGING THE ARM, RAISING IT AND SWINGING IT BACK TO ITS ORIGINAL POSITION.
The movements are effected by pneumatically operated valves and it is essential that the sequence of the valve operations is correct. The present invention is devised to provide a correct and automatic means of providing this sequence. While designed for the particular application of the lifting apparatus referred to above, the invention is not limited to this application and can have many other applications where similar problems are encountered.
The problems to be overcome are those where only a small current is required to operate control members without the use of pilot relays or pilot solenoids and where a reliable resettable stepping sequence operating on a fail safe basis is essential.